A drafting frame for a spinning machine is described, for example, in German patent document DE 197 08 410 A1 and has, at the output side of the drafting frame, a fiber bundling, compaction or condensing zone. Between the output roller pair of the drafting frame and a further feed roller pair delivering the drafted and condensed sliver to the spinning machine, a fiber bundling zone is provided. The fiber bundling zone in this system has a suction shoe over which a perforated belt is looped. The suction shoe is subjected to suction from a suction pump and the perforated belt has a row of perforations to which the sliver is exposed to the suction as the belt passes across the shoe and the sliver lies along the belt. The suction draws any outwardly-projecting fibers into and along the sliver to produce the compaction or condensation effect. The suction through the perforations results in an air flow transverse to the displacement of the sliver to direct the fibers inwardly.
Because of the need for the feed roller pair, a retrofitting of the drafting frame of a conventional spinning machine with a compaction unit is expensive and often impractical.
Another compaction system has been described in German patent document DE 198 46 268 A1, corresponding to U.S. Pat. No. 6,108,873. In this construction the drafting frame is provided at its outlet side with a clamping roller which is driven by one of the output rollers of the drafting frame. The latter output drafting roller and the clamping roller may be coupled together by a transmission unit, for example a gear set or a pulley system. This arrangement has the drawback that the transmission elements are sensitive to contamination and fibers or the like can wind up or accumulate therein. Furthermore, any transmission elements of that type may generate lint or particulates which may be disadvantageous.